1. Field of the Invention
The invention relates generally to an asymmetrical wrench and fastener arrangement having a higher torque in the loosening direction than in the tightening direction, or in the tightening direction than in the loosening direction, for a given amount of applied force. The invention also relates to a wrench and fastener arrangement, wherein there is a higher torque to failure in the tightening direction than in the loosening direction. The invention further relates to an asymmetrical fastener which has a higher torque to failure in one direction than the other, which is stronger than corresponding symmetrical fasteners. Additionally, the invention relates to an asymmetrical spline wrench which can be used with a variety of fasteners.
2. Description of the Prior Art
Fasteners come in a variety of types. For example, there are nuts, which are threaded onto a metal shaft, and bolts, which may threadingly receive a nut or be threadingly received in a bore. Fasteners usually have a head that includes surfaces for loosening and surfaces for tightening. On many fasteners, the loosening surfaces are the same as the tightening surfaces (for example, a hex head nut or bolt). These can be referred to as symmetrical fasteners. Other fasteners utilize surfaces for loosening that are different than the surfaces utilized for tightening. The loosening surfaces and tightening surfaces may be formed on the outer perimeter of the fastener head (hereinafter sometimes referred to as an “external head” or “body”) or on a periphery formed inside of the outer perimeter (hereinafter sometimes referred to as a fastener having an “internal wrench cavity”). The latter fasteners can also be referred to as symmetrical fasteners. External fasteners are designed for use with open-end wrenches or closed end wrenches (or closed wrenches), such as box wrenches or socket end wrenches. Internal fasteners or “closed fasteners” (among which are so called “Allen” fasteners), often referred to as socket head cap screws, are generally designed for use with an internal-key wrench or internal bit. Some wrenches (such as an open-end adjustable wrench) are designed to fit a variety of fastener sizes and configurations.
The periphery on which the loosening surfaces and tightening surfaces of a fastener are formed is sometimes referred to herein as a fastening periphery. While many fasteners have the loosening surfaces and tightening surfaces formed on the same fastening periphery, it is also known to form loosening surfaces on one fastening periphery and tightening surfaces on a different fastening periphery. Such a design has the disadvantages of (1) being relatively expensive, and (2) having a large fastener head which may be too large for practical use in certain applications.
Known wrenches and fasteners have primarily been designed symmetrically, transmitting torque equally in both the tightening and loosening directions. Typical socket wrench types of this kind are shown in FIGS. 1–3, all of which are closed wrenches. FIG. 1 shows a 1½″ hex socket, FIG. 2 shows a 1″ 12-point or double-hex socket, and FIG. 3 shows a 1″ 12-point spline. However, the torque required for loosening a fastener that has been tightened is often several times more than the torque required for tightening a fastener. This is because metal surfaces in contact with one another for an extended period of time tend to seize and resist separation. Another factor that causes the fastener to resist separation is the dissolution of the lubricant that may have been present at the time of tightening. Additionally, tightening of a fastener to near its ultimate strength will cause permanent deformation. This permanent deformation causes the pitch of the threads on the fastener to no longer precisely match the pitch of the nut or the tapped hole. The mismatch requires additional torque to force the threaded elements to conform sufficiently to allow rotation of the fastener. The application of the additional torque required to loosen a fastener can result in system failure (sometimes referred to herein simply as “failure”) prior to the fastener being loosened.
There are numerous modes of fastening system failure. When failure occurs, the mode of failure depends on both the design and physical properties of the wrench and fastener, including their respective strengths, hardnesses and ductilities. A socket wrench may split because of the combined circumferential and radial forces, or its teeth (sometimes referred to herein as protuberances) may shear or bend because of the combination of radial and circumferential forces. The teeth may flow from excessive contact pressure. Further, the points (sometimes referred to herein as corners or protuberances) of the fastener may shear, bend or flow. In addition, in the case of a hollow-head fastener or socket head cap fastener, the fastener head may split due to a combination of radial and circumferential forces, or the wrench may fail in torsion. Existing fasteners and wrenches tend to have a single mode of failure for each particular wrench and fastener. There are numerous modes of failure for both wrenches and fasteners that must be considered so that if steps are taken to strengthen against one failure mode it does not result in increasing the likelihood of another failure mode.
There are various causes of failure in known fastening systems. Many of these problems, such as with double-hex wrenches and double-hex fasteners, are due to points or corners. Corner loading, which results from the engagement of corners on the wrench with the fastener and with corners on the fastener with the wrench, results in wearing down or shearing of the corners and in damage to the surface engaged by the corner. Clearance between the fastener and the wrench results in concentrated force stresses on the fastener and the wrench, and there is a reduced torque resulting from applied force. This load concentration even occurs at normal clearance. Since the fastener is usually at a lower hardness that the wrench, it deforms—and this is aggravated because of the expansion of the wrench under radial loads. The problem is increased with a worn wrench.
Corrosion and paint on fasteners requires increased torque, and concentrated forces can damage the fastener and the wrench. The points on a wrench can be damaged by poor engagement with a fastener. If the fastener is small for the wrench or if the fastener is badly corroded, the wrench may not turn the fastener.
Spline systems have been found to be advantageous in that they can withstand significant amounts of torque. However, a shortcoming of traditional spline fasteners and spline wrenches is that the dimension across the base of the spline is not significantly larger than the dimension near the top of the spline, making the spline susceptible to shear failure.
Failures in traditional wrench and fastener systems have been analyzed, and it has been found that there is significant failure particularly on fastener teeth. This is shown in FIG. 13 and discussed below.
Traditional wrench and fastener systems, such as double-hex systems discussed above, have point-to-point engagement between the point of the wrench and the point of the fastener. This puts force on the points and leads to wearing down of the points of one or both of the fastener and the wrench, limiting their durability and use fitness.
Fastening system failure is expensive because of increased labor and the cost of providing new wrenches and/or fasteners. For example, if a bolt fails the damaged bolt must usually be drilled and removed with special tools. Fastening system failure can also be dangerous because a user applying a great deal of force to a fastener can be harmed when the system fails and his hand or arm may strike a hard or sharp object. Fastener system failure most often occurs when attempting to loosen a fastener because of the greater torque required.
Another problem with traditional wrench and fastener systems, and particularly with spline systems, is that many of these are made with forging techniques. There is considerable difficulty in metal flow in forming the teeth, since the metal must flow into a die, and the flow along surfaces is impeded due to friction between the die surface and the flowing metal. This is particularly acute with spline teeth, since the metal must flow into corners near the base of the fastener or the wrench.
There are many different types of fasteners, wrenches, and systems, many of which are designed specifically for unique applications. For example, there are some systems designed for limiting torque applied in tightening a fastener, some systems designed to show signs when an unauthorized user tampers with a fastener, and some systems designed to apply a maximum amount of torque in turning a fastener, referred to herein as a “high torque” wrenching systems. Additionally, there are many types of configurations for tightening and loosening surfaces of fasteners and wrenches, including but not limited to, hex, double-hex, spline, star and many other fastening configurations. Producing tools made of high strength materials, such as steel, titanium and chromium alloys, and processes required for producing tools with close tolerances result in relatively high production costs and are, consequently, expensive to purchase. A single tool that may be used to turn several differently configured types of fasteners will: (i) reduce the number of tools needed by a user, (ii) reduce time expended by a user on finding different tools to mate; and (iii) reduce an overall investment in the number of tools required by the user.
It would be an advantage to provide a fastening system capable of generating sufficient torque to loosen a fastener, have a fastener and wrench design that can withstand the force of generating such torque without failing, and produce the system in the same dimensions as existing fastening systems.
It would further be an advantage to provide a wrench capable of withstanding the force of high turning torque without failing and also be capable of engaging and driving or loosing fasteners with different types of configurations.
Various wrenches and/or fasteners having ratchet teeth are known, but they differ in structure and in function from the asymmetric splines of the present invention. U.S. Pat. No. 2,685,812 (Dmitroff) discloses a torque nut having an inner nut which is internally threaded and with ratchet-like external teeth. A driving ring is disposed on the outside of the inner nut and has internal ratchet teeth made of a resilient material. As a wrench tightens the outer driving ring, the resilient teeth tighten the inner nut until slippage occurs, and the outer driving ring cannot thereafter tighten the inner nut. A greater force is necessary to loosen the constant torque nut out of necessity. Dmitroff provides an expensive constant torque due to the assembly operation of the resilient teeth of the driving ring and the ratchet teeth, and Dmitroff does not explain if the resilient teeth would also lead to slippage in a loosening operation. Dmitroff does not provide hard metal splines as in the present invention and is directed to providing a constant torque nut, rather than to providing more torque in one direction than in the other to control the loosening or tightening of a splined wrench and/or fastener relative to each other. Moreover, Dmitroff has sharp corners rather than the rounded corners in the present invention for reducing the stress between the fastener and the wrench.
U.S. Pat. No. 5,449,260 (Whittle), like Dmitroff), provides a fastener with a series of connected ratchet teeth. Whittle describes a tamper evident bolt having ratchet teeth on its exterior to receive a special socket to tighten the bolt and interior ratchet teeth in a recess in the head for receiving a ratchet tool for loosening the bolt. The angles of the ratchet teeth are apparently the same. A cap seals the recess. Evidence of tampering is the mutilation of the cap to give access to the interior teeth and mutilation of the exterior teeth if pliers are used to attempt to remove the bolt.
A splined fastener or torque tool is described in U.S. Pat. No. 3,885,480 (Muenchinger). A fastener having splines with radial walls for receiving forces perpendicular thereto to avoid force components not of the torsional effect. The walls are of the same angle for tightening and for loosening. A similar arrangement is shown in U.S. Pat. No. 4,361,412 (Stolarczyk) which discloses a wrenching configuration with spaced radial torque transfer surfaces having a drive angle of 0°. The exterior sides form a hexagon which can also be rotated with a hexagonal wrench.
Another torque-limiting tool is described in German Unexamined First Patent Application DE 40 22 763 A1 (Schneider). Schneider discloses a mechanical screwdriver incorporating a torque limiter having saw tooth-shaped ratchets projecting radially inwardly from a hollow handle and spring elements extending radially outwardly from inside the handle for contacting the steep or low-gradient flanks of the ratchet to establish preset torque values for both directions of rotation.
German Patent 306294 describes a manually-operated screw having saw-toothed shaped teeth which provide less friction to the hand during tightening than during loosening. No wrench is discussed.
Bolts are known whose heads are ruptured when torque of a certain value is reached to make them tamper proof, as in U.S. Pat. No. 5,228,250 (Kesselman). Another such bolt is described in U.S. Pat. No. 5,713,705 (Grünbichler).
U.S. Pat. No. 3,354,757 (Grimm et al.) discloses a spline wrenching system composed of splined wrenches and splined fasteners, each having slightly inclined confronting sides. The configurations are selected to achieve a tendency for mutual failure in shear over their maximum area. The confronting area in both sides of each spline is the same.